MIPS: c-r4k: Avoid duplicate CPU_74K/CPU_1074K checks

MIPS: c-r4k: Avoid duplicate CPU_74K/CPU_1074K checks

Code in a switch statement in probe_pcache checks the CPU type twice
unnecessarily for processor implementations that have the alias removal
feature reported by the CP0 Config7.AR and Config7.IAR bits.  This change
rewrites the affected fragment avoiding the extraneous check and improving
readability.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7221/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>