MdeModulePkg/DriverSample: Skip the character "&" before "OFFSET="

MdeModulePkg/DriverSample: Skip the character "&" before "OFFSET="

When comparing the L"OFFSET=" with the ConfigResp string to find
all the "OFFSET=" in ConfigResp, should skip the character "&"
before "OFFSET=" in ConfigResp string.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>