fs: do not continue on EINTR in file_read_to_end and file_write_all

In case of EINTR, we should return and handle the interrupt. Otherwise,
file_read and file_write will be immediately interrupted again because
of the same pending signal.

kernel/fs/fs.c

@@ -195,8 +195,6 @@ ssize_t file_read_to_end(struct file* file, void* buffer, size_t count) {
     while (cursor < count) {
         ssize_t nread =
             file_read(file, (unsigned char*)buffer + cursor, count - cursor);
-        if (nread == -EINTR)
-            continue;
         if (IS_ERR(nread))
             return nread;
         if (nread == 0)
@@ -234,10 +232,8 @@ ssize_t file_pwrite(struct file* file, const void* buffer, size_t count,
 ssize_t file_write_all(struct file* file, const void* buffer, size_t count) {
     size_t cursor = 0;
     while (cursor < count) {
-        ssize_t nwritten =
-            file_write(file, (unsigned char*)buffer + cursor, count - cursor);
-        if (nwritten == -EINTR)
-            continue;
+        ssize_t nwritten = file_write(
+            file, (const unsigned char*)buffer + cursor, count - cursor);
         if (IS_ERR(nwritten))
             return nwritten;
         if (nwritten == 0)