mtd: remove extra retlen assignment

MTD functions always assign the 'retlen' argument to 0 at the very
beginning - the callers do not have to do this.

I used the following semantic patch to find these places:

@@
identifier retlen;
expression a, b, c, d, e;
constant C;
type T;
@@
(
- retlen = C;
|
T
-retlen = C
+ retlen
;
)

... when != retlen
    when exists

(
mtd_read(a, b, c, &retlen, d)
|
mtd_write(a, b, c, &retlen, d)
|
mtd_panic_write(a, b, c, &retlen, d)
|
mtd_point(a, b, c, &retlen, d, e)
|
mtd_read_fact_prot_reg(a, b, c, &retlen, d)
|
mtd_write_user_prot_reg(a, b, c, &retlen, d)
|
mtd_read_user_prot_reg(a, b, c, &retlen, d)
|
mtd_writev(a, b, c, d, &retlen)
)

I ran it twice, because there were cases of double zero assigments
in mtd tests. Then I went through the patch to verify that spatch
did not find any false positives.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/tests/mtd_stresstest.c

@@ -140,7 +140,7 @@ static int is_block_bad(int ebnum)
 
 static int do_read(void)
 {
-	size_t read = 0;
+	size_t read;
 	int eb = rand_eb();
 	int offs = rand_offs();
 	int len = rand_len(offs), err;
@@ -169,7 +169,7 @@ static int do_read(void)
 static int do_write(void)
 {
 	int eb = rand_eb(), offs, err, len;
-	size_t written = 0;
+	size_t written;
 	loff_t addr;
 
 	offs = offsets[eb];