CHROMIUM: Add #line to pwm.h

Work around coreboot GCC preprocessor bug.

BUG=b:272518464
TEST=BOARD=tentacruel; zmake build --coverage $BOARD &&
./util/find_non_exec_lines.py build/zephyr/$BOARD/output/zephyr.info

Change-Id: I03127ccd29f51faf0ac754f7caf039df0f057939
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5879428
Tested-by: Jeremy Bettis <jbettis@chromium.org>
Reviewed-by: Yuval Peress <peress@google.com>
Commit-Queue: Jeremy Bettis <jbettis@chromium.org>

include/zephyr/drivers/pwm.h

@@ -5,6 +5,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#line 9
 /**
  * @file
  * @brief Public PWM Driver APIs