drivers/char/ipmi/ipmi_si_intf.c: fix warning: variable 'addr_space' set but not used

Fix a warning message generated by GCC, and also updates a web address
pointing to a pdf containing information.

CC [M]  drivers/char/ipmi/ipmi_si_intf.o
drivers/char/ipmi/ipmi_si_intf.c: In function 'try_init_spmi':
drivers/char/ipmi/ipmi_si_intf.c:2016:8: warning: variable 'addr_space' set but not used

Signed-off-by: Sergey V. <sftp.mtuci@gmail.com>
Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Acked-by: Corey Minyard <minyard@acm.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>