kernel: fix compiler warning in mtdsplit_minor.c under 4.4

kernel: fix compiler warning in mtdsplit_minor.c under 4.4

When mtdsplit_minor.c is compiled under Linux 4.4, the compiler
drops the following warning:

    CC      drivers/mtd/mtdsplit/mtdsplit_minor.o
  drivers/mtd/mtdsplit/mtdsplit_minor.c:106:14: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
    .parse_fn = mtdsplit_parse_minor,
                ^
  drivers/mtd/mtdsplit/mtdsplit_minor.c:106:14: note: (near initialization for 'mtdsplit_minor_parser.parse_fn')

The second parameter of the parser function must not have a 'const'
qualifier in 4.4. The 001-mtdsplit_backport.patch removes the qualifier
from other partition parsers. Update it to handle mtdsplit_minor.c as
well.

Signed-off-by: Gabor Juhos <juhosg@freemail.hu>