env: clean env_nvram.c checkpatch and code style

env: clean env_nvram.c checkpatch and code style

Cleanup the env_nvram.c checkpatch warnings, errors and coding style.
There are 2 wanring left about the extern used in c file:
 WARNING: externs should be avoided in .c files
 #53: FILE: env_nvram.c:53:
 +extern void *nvram_read(void *dest, const long src, size_t count);

 WARNING: externs should be avoided in .c files
 #54: FILE: env_nvram.c:54:
 +extern void nvram_write(long dest, const void *src, size_t count);

 total: 0 errors, 2 warnings, 138 lines checked

There is no common nvram header file to use instead of the externs.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>