WPS ER: Fix SSDP CACHE-CONTROL line parser

WPS ER: Fix SSDP CACHE-CONTROL line parser

Incorrect number of bytes was skipped from the beginning of the line
which resulted in the loop skipping spaces doing nothing. However, the
following operation was simply looking for the max-age parameter with
os_strstr(), so this did not have any effect on functionality. Fix the
number of bytes to skip and remove the unneeded loop to skip spaces.

Signed-off-by: Jouni Malinen <j@w1.fi>