Blackfin arch: add proper ENDPROC()

add proper ENDPROC() to close out assembly functions
so size/type is set properly in the final ELF image

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>

arch/blackfin/lib/modsi3.S

@@ -77,3 +77,5 @@ ___modsi3:
 	R0 = 0;
 .LRETURN_R0:
 	RTS;
+
+.size ___modsi3, .-___modsi3