Fix incorrect condition in initramfs_tool_helper() path argument handling

[dkeven]

Fix a logic error in initramfs_tool_helper() where the path argument handling used a single if/else with a combined outer condition if (path && path_specific_args), causing two distinct issues:

1. Spurious warning in the common case:
   When the tool is update-initramfs (path_specific_args = NULL, requires_path = FALSE) and an initramfs image such as /boot/initrd.img-<kernel> exists, the first attempt always falls through to the else branch where !path evaluates to true (since path is NULL on the first call), producing a misleading warning:
   "/usr/sbin/update-initramfs requires a file path argument, but none was given."
   The command only actually runs on the second attempt.
2. Complete failure in less common configurations:
   When executed on a machine where /boot contains only initrd.img without a kernel-versioned suffix, get_initramfs_path() returns NULL for all attempts. Since the else branch condition requires_path || !path is always true when path is NULL, all 4 retry attempts emit the same warning and update-initramfs is never executed, resulting in:
   "Failed to rebuild the initramfs!".

This also removes a dead code path where !path_specific_args was checked inside a block that already required path_specific_args to be non-NULL.

I've built nvidia-installer and tested this fix myself, and update-initramfs -u executes successfully on the first
attempt in both scenarios described above.