m32r: fix build warning about putc

We were getting build warning:

  arch/m32r/boot/compressed/m32r_sio.c:11:13:
     warning: conflicting types for built-in function 'putc'

Here putc is used as a static function so lets just rename it to avoid
the conflict with the builtin putc.

Link: http://lkml.kernel.org/r/1466977046-24724-1-git-send-email-sudipm.mukherjee@gmail.com


Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>