scripts/checkpatch: Fix typo in SPDX-License-Identifier keyword

Fix the typo in the error message to help `grep` the example:

ERROR: New file '***' requires 'SPDX-License-Identifer'

Fixes: fa4d79c64dae ("scripts: mandate that new files have SPDX-License-Identifier")
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-ID: <20250408162702.2350565-1-zhao1.liu@intel.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

scripts/checkpatch.pl

@@ -1688,11 +1688,11 @@ sub process {
 			    /\.(c|h|py|pl|sh|json|inc|Makefile)$/) {
 			    # source code files MUST have SPDX license declared
 			    ERROR("New file '$expect_spdx_file' requires " .
-				  "'SPDX-License-Identifer'");
+				  "'SPDX-License-Identifier'");
 			} else {
 			    # Other files MAY have SPDX license if appropriate
 			    WARN("Does new file '$expect_spdx_file' need " .
-				 "'SPDX-License-Identifer'?");
+				 "'SPDX-License-Identifier'?");
 			}
 		    }
 		    $expect_spdx = 1;