powerpc/nvram_64: Check nvram_error_log_index in nvram_clear_error_log()
powerpc/nvram_64: Check nvram_error_log_index in nvram_clear_error_log()

nvram_clear_error_log() calls ppc_md.nvram_write() even when
nvram_error_log_index is -1 (invalid). The nvram_write() function does
not check for a negative offset.

Check nvram_error_log_index as the other nvram log functions do.

Signed-off-by: Thomas Gleixner <00e4cf8f46a57000a44449bf9dd8cbbcc209fd2a@linutronix.de>
Cc: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>
Cc: 624e0123bdcc7ea450e9efbcd399e8858e365d3e@ozlabs.org
Signed-off-by: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas