Change dummy variable in mpih-div.c to mpi_limb_t type

* mpi/mpih-div.c (_gcry_mpih_mod_1, _gcry_mpih_divmod_1): Change dummy
variable to 'mpi_limb_t' type from 'int'.

Patch attempts to fix problem reported by Matthias Wachs:

while updating our buildbots I got another compile error:

On a OS X machine:

Darwin luke.net.in.tum.de 11.3.0 Darwin Kernel Version 11.3.0: Thu Jan
12 18:47:41 PST 2012; root:xnu-1699.24.23~1/RELEASE_X86_64 x86_64

/bin/sh ../libtool --tag=CC --mode=compile gcc -DHAVE_CONFIG_H -I.
-I.. -I../src -I../src -I/opt/local/include -I/opt/local/include -g -O2
-Wall -MT mpih-div.lo -MD -MP -MF .deps/mpih-div.Tpo -c -o mpih-div.lo
mpih-div.c
libtool: compile: gcc -DHAVE_CONFIG_H -I. -I.. -I../src -I../src
-I/opt/local/include -I/opt/local/include -g -O2 -Wall -MT mpih-div.lo
-MD -MP -MF .deps/mpih-div.Tpo -c mpih-div.c -fno-common -DPIC -o
.libs/mpih-div.o
mpih-div.c: In function '_gcry_mpih_mod_1':
mpih-div.c:183: error: unsupported inline asm: input constraint with a
matching output constraint of incompatible type!
make[2]: * [mpih-div.lo] Error 1
make[1]: * [all-recursive] Error 1
make: *** [all] Error 2

The new x86-64 inline assembly for MPI expects outputs to be limb sized
variables (64-bit), but mpi/mpih-div.c was using 32-bit dummy variable.
Appearently this mismatch between assembly output and variable sizes does not
fail on every platform.

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>