main/postmarketos-initramfs: wait for boot partition

Some devices take time to initialize storage, e.g. Qualcomm laptops using ADSP need to load firmware firstly, and initramfs script does not always manage to mount boot partition in time.

Unfortunately, there is no reliable way to reproduce the issue, but this patch should fix cases like this.

main/postmarketos-initramfs/APKBUILD

@@ -88,7 +88,7 @@ sha512sums="
 ab41b45b0613f25a61114ed8c8b92bc53c60838f6e2e0ba18c76e5369b2984e6023a0661887692673aca3f647f268c468a468f6b1ac424cfee609017a89481dd  00-initramfs-base.files
 8a4adad3785af474b36a09a05f6a3b2c4b4f43aac331a53b903abfa51ea12be1e3d1d807b7a6e66a1346815f3b0044daf8cd62e21e2dc75d2db13ee265a72985  00-initramfs-extra-base.files
 b1462989633c65a102e7ae7ced9c41a00673b4c7434cd3fe16c229c39bb870d7e850b0d317487191b7d7ca32c75b2eed1561b1facf405bd4d876d32c71badcf3  init.sh
-199c997ecb7f6666cddc2552cecb86613105992f4868394bba367a2e3c0847b40d0fc9556c91eca3eebac8330595ebe80a95fba84a462a81cc183c713c48ca44  init_functions.sh
+f960b85a04f41c5e3ec1ce1aca21b00ab13a574b779390cffbe0b08e7c0f13479c987becfee2a1853276f5704ab1bdc371ada456b4298d9064d24f249770f996  init_functions.sh
 ba3275a9af788c7c782322a22a0f144d5e50e3498ea6886486a29331f23ae89cd32d500a3635cfa7cab369afba92edc18aeca64ccbf0cd589061cce23d15b46c  unudhcpd.conf
 675e7d5bee39b2df7d322117f8dcaccc274d61beaf4d50ead19bbf2109446d64b1c0aa0c5b4f9846eb6c1c403418f28f6364eff4537ba41120fbfcbc484b7da7  mdev.conf
 "