Fix PRU GAS for 32-bit hosts

Fix PRU GAS for 32-bit hosts

The PRU GAS port I originally submitted does not build on 32bit hosts.
This patch fixes it by aligning md_number_to_chars's definition with
the global declaration in tc.h.

Here is the original bug report I got:
  https://github.com/rcn-ee/repos/pull/23#issuecomment-269915175

	* config/tc-pru.c (md_number_to_chars): Fix parameter to be
	valueT, as declared in tc.h.
	(md_apply_fix): Fix to work on 32-bit hosts.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>