util/ecst: check fseek/ftell return values
util/ecst: check fseek/ftell return values

Found by Coverity Scan #5814[14-9], #58159, #58160

Also fix a bunch of typos in comments and variable names and remove
extraneous fseek(..., 0, SEEK_SET) before moving to the actual offset
(again with SEEK_SET).

BUG=none
BRANCH=none
TEST=none

Change-Id: I9d7cb950a7a659c5abb1ff7d6d2c48d623ee515c
Signed-off-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1789145
Tested-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>
Auto-Submit: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Commit-Queue: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec