arm_adi_v5: fix scan-build warning [1/3]

arm_adi_v5: fix scan-build warning [1/3]

Commit 21f7885d1c2a ("arm_adi_v5: separate ROM table parsing from
command output [1/3]") introduces a new scan-build warning because
continues the execution even when dap_get_debugbase() returns
error. The value of 'apid' can be uninitialized:

	5th function call argument is an uninitialized value

Check the return value and quit on error.
While there, remove the useless initialization of 'dbgbase' that
was apparently required for the same problem.

Change-Id: Iade26a152925ee0f1bf114ed829b94f7ed5b254f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Fixes: 21f7885d1c2a ("arm_adi_v5: separate ROM table parsing from command output [1/3]")
Reviewed-on: https://review.openocd.org/c/openocd/+/7010
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>