MIPS: IP22: Fix GCC 4.6.0 build error

  CC      arch/mips/sgi-ip22/ip22-platform.o
arch/mips/sgi-ip22/ip22-platform.c: In function 'sgiseeq_devinit':
arch/mips/sgi-ip22/ip22-platform.c:135:15: error: variable 'tmp' set but not used [-Werror=unused-but-set-variable]
cc1: all warnings being treated as errors

While at it rename the variable to pbdma for readability; there is a
local variable tmp of different type being used in two nested blocks.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>