scripts/spelling.txt: add regsiter -> register spelling mistake

This typo is quite common.  Fix it and add it to the spelling file so
that checkpatch catches it earlier.

Link: http://lkml.kernel.org/r/20170317011131.6881-2-sboyd@codeaurora.org
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/m68k/ifpsp060/src/ilsp.S

@@ -776,7 +776,7 @@ muls64_zero:
 # ALGORITHM ***********************************************************	#
 #	In the interest of simplicity, all operands are converted to	#
 # longword size whether the operation is byte, word, or long. The	#
-# bounds are sign extended accordingly. If Rn is a data regsiter, Rn is #
+# bounds are sign extended accordingly. If Rn is a data register, Rn is #
 # also sign extended. If Rn is an address register, it need not be sign #
 # extended since the full register is always used.			#
 #	The condition codes are set correctly before the final "rts".	#

arch/m68k/ifpsp060/src/isp.S

@@ -1876,7 +1876,7 @@ movp_read_err:
 # word, or longword sized operands. Then, in the interest of		#
 # simplicity, all operands are converted to longword size whether the	#
 # operation is byte, word, or long. The bounds are sign extended	#
-# accordingly. If Rn is a data regsiter, Rn is also sign extended. If	#
+# accordingly. If Rn is a data register, Rn is also sign extended. If	#
 # Rn is an address register, it need not be sign extended since the	#
 # full register is always used.						#
 #	The comparisons are made and the condition codes calculated.	#